In connection with the manufacture of endless power transmission belts, such as V-belts, gear belts, and the like, it is conventional to utilize a construction of fabric reinforced rubber or other elastomer. Typically, the belt structure includes a cord winding layer, which is located along the "neutral" axis of the belt. Cross sectional areas of the belts above and below the neutral axis are subject to flexing in tension and/or compression. In a typical endless belt, for example, outer portions of the belt cross section are flexed in tension, as the belt passes around the sheaves over which it is trained. The inner cross sectional portion of the belt are subjected to flexing in compression. For some installations, a single belt may be required to pass over both internal and external sheaves, such that both the inner and outer cross sectional portions thereof are flexed in both tension and compression.
In a transmission belt of conventional construction, strips of reinforcing fabric are incorporated into the elastomeric material of the belt, in the inner and outer cross sectional areas thereof, to impart stability to the belt geometry. Since these areas of the cross section undergo flexing in tension and/or compression, it has been customary to utilize bias-type fabric for the reinforcing material, so that the yarns of the fabric do not extend parallel to the longitudinal axis of the belt, but are arranged at angles thereto. Such reinforcing fabrics can be either wrapped around the exterior of the belt or incorporated internally thereof, or both.
Pursuant to prior practice, the manufacture of bias-type reinforcing fabric has been extremely labor intensive, and therefore costly, and at the same time less than optimally effective for the purpose. In one commonly used procedure, for example, tubular woven fabric is slit along a spiral at an angle of about 15.degree. to the longitudinal axis of the fabric tube. The continuous strip resulting from the bias slitting of the tube has its yarns disposed asymmetrically with respect to the longitudinal axis of the fabric strip. The slit fabric strip is thereafter elongated to reorient the yarns, in an effort to align them approximately at a relative angle of about 120.degree.. The length of slit fabric is impregnated with uncured elastomeric material and then banner cut into short sections, at an angle of about 60.degree. to the axis of the warp yarns in the slit fabric. The banner cutting results in a series of rhomboid-shaped sections. These are rotated 90.degree. and then spliced by overlapping. This results in a spliced length of material, in which the yarns are arranged at an angle of around 120.degree., symmetrical to the longitudinal axis of the spliced length. This assembled length is later slit into narrower strips, appropriate to the desired end use.
Because of crowding of the yarns at the edge extremities of the tubular woven material, a continuous length of the bias cut fabric has periodic diagonal non-uniformities. If allowed to remain in the fabric, these can result in undesirable puckering, bagging or wrinkling. Accordingly, it is sometimes necessary to cut away and discard these sections before banner cutting.
It will be readily apparent from the above that the manufacture and installation of conventional reinforcing materials is a significant labor factor in the manufacture of a power transmission belt. Bias fabrics manufactured in conventional ways have several additional inherent disadvantages. For one, the yarn angles, which ideally are normally about 120.degree. (60.degree. to the longitudinal axis), are very difficult to obtain and control with conventional, tubular woven fabrics. Precision in achieving the desired angle is difficult, and maintaining the angle thereafter during the manufacturing process is also difficult.
The present invention is directed to a novel and advantageous procedure for the manufacture of reinforcing fabrics, especially for transmission belts, hoses and the like, which is not only significantly more economical to produce than conventional fabrics, but provides a far superior component to the belt/hose manufacturer.
Pursuant to the present invention, the reinforcing fabric is not woven in tubular form, but is woven in flat form, advantageously on a high speed shuttleless machine. The woven starting material is more or less conventional in form, advantageously being of a poly/cotton composition. The particular yarn composition and fabric makeup can be varied to suit the requirements of the end user and is not, per se, a part of the present invention.
A conventionally flat woven fabric is further processed pursuant to the invention to impart thereto a significant bias construction. That is, the weft yarns are caused to be disposed at a substantial angle to the longitudinally extending warp yarns. Ideally, the weft yarns, after preliminary processing, are disposed at an angle of approximately 120.degree. to the warp yarns. This is accomplished most advantageously by the use of a set of angularly disposed rollers, which cause one selvege of the woven fabric to be displaced and retarded, relative to the other, in the course of linear movement of the web during processing.
Pursuant to the invention, the fabric, after weaving, is directed through a treating bath wherein it is wet sufficiently to soften the sizing agent in the fabric. Thereafter, the fabric is subjected to a procedure, by angled rollers, special differential tentering, etc., in order to displace one selvege substantially with respect to the other in the longitudinal direction, to cause the weft yarns to be disposed at a 120.degree./60.degree. angle to the warp yarns. The fabric is then retained in this condition while dried and stabilized.
After drying, the fabric advantageously is subjected to an edge slitting operation, most desirably by hot knives at each side, in order to remove the selvege portions. In this condition, the fabric can be rolled up and shipped to the belt/hose manufacturer.
The reinforcing fabric, which is the subject of the invention, is far superior to conventional tubular woven fabrics processed in the conventional way. Not only is the processing technique according to the invention significantly more economical, but it greatly simplifies the operations required by the belt/hose manufacturer and enables the product manufacturer to achieve a superior product.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention, and to the accompanying drawing.